a) Field of the Invention
The invention is directed to an arrangement for detecting the position of two bodies moving relative to one another by means of a light barrier system, wherein a device is arranged on at least one of the moving bodies such that when the bodies move relative to one another there is a change in the signal of the light barrier system that can be evaluated.
Such positioning systems are used, for example, in microscopy, where adjusting paths for the adjustment of diaphragms are in the millimeter range.
b) Description of the Art
A number of positioning arrangements aiming at adjusting and measuring paths in the millimeter range by means of light barriers are known from the prior art. In enclosed construction, light barriers are used as fork light barriers and reflection light barriers. In open construction, light transmitters and light receivers are spatially separated. Light barriers are used primarily for switching functions. Light barriers are used for path measurements through the use of lugs or tags in fork light barriers or reflectors in reflection light barriers. Miniaturized SMD components are used as light barriers and, while inexpensive, ensure measurement ranges only in the millimeter range. Hall probe path measurement systems, known in general, have a higher accuracy, but have the disadvantage of a relatively high sensitivity of the construction of the overall system to magnetic fields, oscillations, vibrations and temperature changes.
Further, the firm of Dr. Johannes Heidenhain GmbH, for example, offers a number of numeric measurement systems which measure a movement of bodies relative to one another for use in the field of mechanical engineering. Accuracies of less than 1 xcexcm in measuring and adjusting ranges of about 100 mm are possible with these measuring systems, but the technical expenditure for these measuring systems, and therefore the price, is relatively high.
It is further known to measure the elastic deformability of the skin with a light barrier (DE-A-38 32 690). It is disadvantageous in this arrangement that measurement ranges of only about 1 mm and resolutions of only xe2x89xa710 xcexcm can be achieved and that the measurement signals of the light barrier are corrupted by temperature influences and drift.
Based on the prior art mentioned above, it is the primary object of the invention to realize an arrangement for detecting the change in position between two bodies moving relative to one another which has a relatively high positioning accuracy, is relatively compact, can be produced and assembled economically and can detect adjusting steps in a range of less than 1 xcexcm.
According to the invention, this object is met in an arrangement of the kind mentioned above in that at least one pair of light barrier systems are connected with one another directly or via an electronic circuit and are associated with the device arranged on the bodies. According to a preferred construction of the invention, each pair of light barrier systems interacts with the device, resulting in increased sensitivity, linearization of the characteristic line and at least partial compensation of interference in the signals to be evaluated.
In an advantageous further development of the invention, the device is constructed as a diaphragm. Further, in order to achieve large measurement paths, it is advantageous when the light barrier systems are arranged so as to be fixed relative to one another and the body moving relative to the latter is provided with at least one diaphragm in the form of a wedge, each wedge passing through at least one associated pair of light barrier systems. Further, it is also advantageous to design the reflection characteristics or transmission characteristics of the diaphragm so as to be spatially dependent.
Further, drift compensation of the light barrier systems is preferably carried out by means of an electronic circuit. According to another preferred development of the invention, drift compensation is provided for each light barrier system. In another advantageous construction of the invention, drift compensation can be carried out by means of software correction.
Further, the light barrier systems are preferably operated in AC.
In the following, the invention will be described more fully by way of example with reference to schematic drawings.